Certain dental procedures involve taking an impression of a dental arch, using the impression to create a cast of the arch, and using the cast to fabricate an appliance for the arch. In some cases full arch impressions are taken of both arches, in others only one arch is involved, and in still others only partial arch impressions are taken. Common to all of these however is the necessity that the impression material taken an impression that includes the crowns of teeth and at least the adjoining gum margin.
The prevailing clinical practice for taking an impression of a dental arch comprises the use of an outer tray conforming to the shape of the arch that is filled with an impression taking material. This outer tray is typically metal although non-metal trays are known. The impression taking material is typically a clay like composition that is initially soft when placed intra-orally and that hardens around the arch after the arch is impressed into it. This material is alginate, and it is the typical clinical practice for the material to be prepared in the dentist's office and placed in a tray just prior to the taking of a patient's impression. The dentist and staff must devote time to this preparation and often to holding the tray engaged with the patient's arch while the impression taking material sets. Moreover, anyone who has been treated by this procedure is apt to agree that the process is rather unpleasant, and this is due to a large extent to the nature of the impression taking material. A further aspect of using such material is that it takes at least several minutes to set, and once it has set, it cannot be re-softened.
In spite of certain characteristics that are generally considered undesirable, this prevailing clinical practice has continued for quite a few years without significant change. As mentioned above, plastic outer trays are known, and in at least one instance it has been proposed to use such a tray directly for taking an arch impression. U.S. Pat. No. 4,569,342 discloses such a tray, which is also alleged to be suitable for subsequent use by the patient as a dental The tray of that patent is described to be made of methacrylic hexyl ester. Other U.S. Pat. Nos. relating to arch impression devices are: 2,845,708; 3,302,289; and 3,537,179. Other patents that relate to plastic trays used for other purposes such as application of medicinal compositions are: U.S. Pat. Nos. 3,955,281; and 4,173,505.
The present invention relates to a new and unique impression tray assembly for taking an impression of a dental arch including the crowns of teeth and at least the adjoining gum margin, such impression tray assembly being characterized by a multi-laminar impression taking material wherein one lamina has characteristics different from those of another lamina. According to a preferred embodiment of the invention, these two lamina are ethylene vinyl acetate of different durometers and one lamina is injection-molded onto the other. The one lamina that is injection-molded onto the other has a lower durometer than that of the other. This lower durometer lamina is for facing the arch whose impression is to be taken while the higher durometer lamina is for facing an even higher durometer tray that holds the multi-laminar impression taking material. While it may be possible for the multi-laminar impression taking material to simply be placed into the tray, it is believed that a better device is created by having the impression taking material bonded to the tray. Accordingly, a preferred method for fabricating a device according to to principles of the invention is to injection mold the higher durometer lamina of the impression material directly onto the tray, and then injection mold the lower durometer lamina of the impression taking material onto the higher durometer lamina of the impression taking material.
The invention offers important advantages over the prevailing practice. First, the device can be fabricated in a hygienic environment and packaged in a hermetically sealed enclosure. The enclosure is opened only prior to use so that the hygienic integrity of the device is assured, both to the dentist and the patient. The device is prepared for use by heating it to an extent sufficient to render the impression taking material sufficiently soft and formable so that the desired arch impression can be taken. The device is then intra-orally placed onto the arch and held there for an amount of time that will assure that details of the arch impression will not be lost due to deformation or distortion during removal of the device from the arch. This can be a shorter time than is required under the currently prevailing practice.
Another advantage is that the procedure is less unpleasant for the patient. Placement of a warm plastic device onto an arch is believed appreciably less objectionable than placement of a device with a mass of claylike material in a cold and hard metal tray. It is also believed that a patient will be less prone to gagging, and the impression taking material of the invention can, if desired, be provided with an agreeable flavoring, such as mint.
The applicant's development of the invention has revealed that exceptionally fine detail can be obtained in an impression due to the particular materials that are used in the presently preferred embodiment that is described in detail herein, although it is to be understood that principles of the invention are in some respects broader than these particular materials. It is believed that what may be described as a synergistic effect is obtained through the multi-laminar construction of the impression taking material using a relatively low durometer, relatively high vinyl acetate content for the lamina that is to face the arch and a somewhat higher durometer ethylene vinyl acetate for the adjoining lamina onto which the former lamina is injection molded. While the use of ethylene vinyl acetate is not broadly new in intra-oral devices, it is believed that the Applicant is the first to recognize that it can be used in an impression tray for taking an impression of a dental arch that includes the crowns of teeth of the arch and at least the adjoining gum margin. Moreover, it is believed that the use of the multi-laminar construction for the impression taking material and the creation of a multi-laminar assembly which comprises beth the multi-laminar impression taking material and an outer plastic tray are also utterly novel. The use of the particular relatively low durometer, relatively high vinyl acetate content for the lamina that faces the arch is also believed a further utterly novel feature.
The forgoing advantages and features, along with additional ones, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.